The present application relates to components for interfacing a plurality of detector elements to detector modules. More particularly, the invention relates to means for interfacing thin film detector elements to a multi-layer structure having layers disposed transverse to the plane to the detector elements.
The infrared spectrum covers a range of wavelengths longer than the visible wavelengths but shorter than microwave wavelengths. Visible wavelengths are generally regarded as between 0.4 and 0.75 micrometers. The near infrared wavelengths extend from 0.75 micrometers to 10 micrometers. The far infrared wavelengths cover the range from approximately 10 micrometers to 1 millimeter. The function of infrared detectors is to respond to energy of a wavelength within some particular portion of the infrared region.
Heated objects will dissipate thermal energy having characteristic wavelengths within the infrared spectrum. Different levels of thermal energy, corresponding to different sources of heat, are characterized by the emission of signals within different portions of the infrared frequency spectrum. No single detector is uniformly efficient over the entire infrared frequency spectrum. Thus, detectors are selected in accordance with their sensitivity in the range of interest to the designer. Similarly, electronic circuitry that receives and processes the signals from the infrared detector must also be selected in view of the intended detection function.
A variety of different types of infrared detectors have been proposed in the art since the first crude infrared detector was constructed in the early 1800's. Virtually all contemporary infrared detectors are solid state devices constructed of materials that respond to infrared frequency energy in one of several ways. Thermal detectors respond to infrared frequency energy by absorbing that energy causing an increase in temperature of the detecting material. The increased temperature in turn causes some other property of the material, such as resistivity, to change. By measuring this change the infrared radiation is measured.
Photo-type detectors (e.g., photoconductive and photovoltaic detectors) absorb the infrared frequency energy directly into the electronic structure of the material, inducing an electronic transition which, in turn, leads to either a change in the electrical conductivity (photoconductors) or to the generation of an output voltage across the terminals of the detector (photovoltaic detectors). The precise change that is effected is a function of various factors including the particular detector material selected, the doping density of that material and the detector area.
By the late 1800's, infrared detectors had been developed that could detect the heat from an animal at one quarter of a mile. The introduction of focusing lenses constructed of materials transparent to infrared frequency energy, as well as advances in semiconductor materials and highly sensitive electronic circuitry have advanced the performance of contemporary infrared detectors close to the ideal photon limit.
Current infrared detection systems incorporate arrays of large numbers of discrete, highly sensitive detector elements the outputs of which are connected to sophisticated processing circuitry. By rapidly analysing the pattern and sequence of detector element excitation, the processing circuitry can identify and monitor sources of infrared radiation. Though the theoretical performance of such systems is satisfactory for many applications, it is difficult to actually construct structures that mate a million or more detector elements and associated circuitry in a reliable and practical manner. Consequently, practical applications for contemporary infrared detection systems have necessitated that further advances be made in areas such as miniaturization of the detector array and accompanying circuitry, minimization of noise intermixed with the electrical signal generated by the detector elements, and improvements in the reliability and economical production of the detector array and accompanying circuitry.
A contemporary subarray of detectors may, for example, contain 256 detectors on a side, or a total of 65,536 detectors, the size of each square detector being approximately 0.0035 inches on a side, with 0.0005 inches spacing between detectors. The total width of such a subarray would therefore be 1.024 inches on a side. Thus, interconnection of such a subarray to processing circuitry requires a connective module with sufficient circuitry to connect each of the 65,536 detectors to processing circuitry within a square a little more than one inch on a side. The subarrays may, in turn, be joined to form an array that includes 25 million detectors or more. Considerable difficulties are presented in aligning the detector elements with conductors on the connecting module and in isolating adjacent conductors in such a dense environment.
Where the array material is very thin, less than 0.005 inches, difficulties arise in attaching the array material to the face of the module. Such difficulties may be attributed to a variety of reasons including the inability of the detector material to absorb forces generated by the mismatched coefficient of expansion between the module and the array material. This mismatch in the expansion coefficients is particularly problematical where the detector is formed of material such as solid state recrystallized bulk mercury cadmium telluride.
Additional difficulties have been encountered in providing a means for testing the reliability of the individual detector elements. Where the detector material is applied directly to the module body it is difficult to isolate a fault that may be attributable to either the detector elements, module wiring or processing elements. Where the detector elements are not testable apart from the module body the testing and assembly process becomes substantially less reliable and result in the production of assemblies that may be useless or expensive to repair.
The present invention is directed to the construction that remedies these and other deficiencies in the construction of contemporary infrared detector modules. The invention provides a technique in construction that facilitates testability of the detector elements prior to securing the elements to the connecting module. The invention also provides a structure that reduces the sensitivity of the detector material to expansion or contraction of the detector module.